The present invention relates to a process and apparatus for preheating combustion mediums, for example combustion air and fuel gas. More specifically, the present invention relates to such a process and apparatus for preheating such combustion mediums used for firing blast furnace stoves by utilizing the heat of waste gases resulting from such firing.
The overall efficiency of a blast furnace stove is heavily dependent upon the thermal use of the waste, flue or exhaust gases produced during firing of the blast furnace stoves and coming from the checker work or checker shafts at a temperature which is still relatively high, if the size of the blast furnace stove is to be maintained within practical limits. Accordingly, the heat content of the waste gases resulting from the firing of the blast furnace stoves is utilized, for example in heat exchangers for preheating fuel gas and the combustion air employed for heating or firing of the blast furnace stoves. A problem with such arrangement is that the waste gases, after passing through the heat exchangers, are at a temperature below the dew point temperature. This may result in corrosion of the waste gas lines, in the waste heat flue, in the stack and in the colder heat exchange components, thus leading to premature failure of one or more of such elements. If extreme temperature fluctuations of the waste gases emerging from the blast furnace stoves continue to occur, it is necessary to maintain the waste gas temperature on the entry side of the stack relatively constant in order to save energy and also to prevent the dew point from dropping below a predetermined value.